Half orig fee res | Matt example (#966)

* added Matts test as proof that attack no longer works on his branch

* Revert "Remove multicall from position manager (#948)" (#961)

This reverts commit f540c8a.

* added test testSpendOrigFeePushBadDebtToBorrowers test

* cleaned up testStealReservesWithMarginm to match minted balances

* responded to Matts comments

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Co-authored-by: Ian Harvey <[email protected]>
Co-authored-by: Mike Hathaway <[email protected]>